Is it possible to change another person's behavior—and transform a less-than-perfect relationship—simply by changing your own thoughts? Psychologist Henry Grayson's theory may very well revolutionize the way we look at love, friendship, and attachment.

In his heretical book, Mindful Loving, Henry Grayson, an eminent New York psychologist, relates a story that perfectly captures his mind-altering theory of love. A despondent patient had come to Grayson's office, complaining about being married to "the world's biggest shrew." As patients frequently do, Jon seemed to want commiseration from his loyal shrink.

Grayson isn't that kind of doctor. "What are you willing to do?" asked the therapist, turning the tables back on Jon.

"Anything," he replied. Grayson's instructions were oddly simple: The next time Jon became anxious over his wife's behavior, he was to focus on his own upsetting thoughts, replacing the inner wife-hating voice—"She's ruining my life!"—with a tender memory of the woman he'd once loved. At first Jon couldn't recall such a woman; finally, a happy moment oozed up from the distant past. He promised Grayson he'd give it a try.

Jon was confused at his next appointment. He told Grayson his wife seemed more subdued somehow. "She must be coming down with a bug," Jon said.

"Try the experiment again," Grayson suggested.

At the following session, Jon was genuinely suspicious. He and his wife had spent their first tirade-free weekend at home in years. Perhaps she'd begun to see a therapist, Jon said, still failing to connect the dots. But a week later, Jon realized that the internal shift in his attitude had created the external shift in his wife's attitude.

The notion that relationships succeed or fail according to how we think about them may seem far-fetched. The science of relationships has tended to emphasize modifying outward behavior—which is why, according to Grayson, most couples therapy doesn't work. "It's like trying to clean up a river downstream rather than at its source," he says, settling his rangy, handsome self—think Mr. Rogers much better dressed—into the nook of a pale leather sofa. "We have to go upstream to what we're thinking—to the beliefs and behavior that come from our thoughts—instead of trying to change our emotions or, even worse, other people's behavior."

This principle applies to all relationships and not merely to the ones we call special. Specialness makes loving more difficult, Grayson claims—counterintuitive though that may sound—since casting people in the role of lover, mentor, spouse, or best friend raises expectations, which leads to fantasy, heartbreak, and pain. We suffer at the hands of those we love the most—that's the conundrum. "So much expectation," says Grayson, "blinds us to love."

There are two forms of attachment, apparently, both of which are known by the L word but which, in fact, are very different. "There's ego-based love," he tells me, using ego not to denote the Freudian sense of self that's indispensable to negotiating daily life but to refer to the illusory armor that suffocates and cuts us off, the self-obsessed me that renders us so unspeakably lonely, stripped of the feelings of belonging and connection. "That's the irony," Grayson says. "First we imagine our separation from others, then we spend our precious lives trying, and failing, to bridge this false divide."

Spiritual love works on an opposite principle, he continues. Instead of the doomed attempt to "complete" ourselves through another person—the ego being chronically hungry, unworthy, unsatisfied—spiritual relationships hinge on the knowledge that each of us is already whole. "We're complete," Grayson insists, joining his fingers to form a circle. "We are made from the very same energy as the rest of creation—love, as it is called in the gospels—in its myriad forms. Our essential nature is divine. In other words, we are already this wholeness, this love, that we seek outside ourselves."

To appreciate how an agnostic scientist came to this mystical understanding, we need to trace Grayson's pilgrim's progress from choirboy to quantum clinician. Born 68 years ago in Alabama, he'd planned to become a Protestant minister till a few months in theology school convinced him that he had no faith—not of the church-approved kind, anyway. "I had stopped believing in the traditional concepts of a medieval, flat-earth 'sky God,' a deity that was far removed from us humans here on earth," he writes in the preface to his book. Grayson completed his studies nevertheless, earning degrees in psychology and pastoral counseling, then worked briefly as a parish minister, struggling to reconcile traditional teachings with his desire to help his congregants feel God in "every aspect of their lives."